According to United States Golf Association (U.S.G.A.) rules, a golf ball may not have a weight in excess of 1.620 ounces or a diameter smaller than 1.680 inches. The initial velocity of U.S.G.A. “regulation” balls may not exceed 250 feet per second with a maximum tolerance of 2%. Initial velocity is measured on a standard machine maintained by the U.S.G.A. wherein a projection on a wheel rotating at a defined speed hits a test ball, and the period of time it takes the ball to traverse a set distance after impact is measured. U.S.G.A. regulations also require that a ball not travel a distance greater than 280 yards when hit by the U.S.G.A. outdoor driving machine under specified conditions. In addition to this specification, there is a tolerance plus 4% and a 2% tolerance for test error.
These specifications limit how far a golf ball will travel in several ways when hit. Increasing the weight of a golf ball tends to increase the distance it will travel and lower the trajectory. A ball having greater momentum is better able to overcome drag. Reducing the diameter of the ball also has the effect of increasing the distance it will travel when hit. This is believed to occur primarily because a smaller ball has a smaller projected area and thus, a lower drag when traveling through the air. Increasing the initial velocity increases the distance the ball will travel.
The foregoing generalizations hold when the effect of size, weight, or initial velocity is measured in isolation. Flight characteristics primarily (influenced by dimple pattern and ball rotation properties), club head speed, radius of gyration, and diverse other factors also influence the distance a ball will travel.
In the manufacture of top-grade golf balls for use by professional golfers and amateur golf enthusiasts, the distance a ball will travel when hit (hereinafter referred to as “distance”) is an important design criterion. Since the U.S.G.A. rules were established, golf ball manufacturers have designed top-grade U.S.G.A. regulation balls to be as close to the maximum weight, minimum diameter, and maximum initial velocity as golf ball technology will permit. The distance a ball will travel when hit has, however, been improved by changes in raw materials and by alterations in dimple configuration.
Golf balls not conforming in various respects to U.S.G.A. specifications have been made in the United States. Prior to the effective date of the U.S.G.A. rules, balls of various weights, diameters, and resiliencies were common. So-called “rabbit balls,” which claim to exceed the U.S.G.A. initial velocity limitations, have also been offered for sale. Recently, oversized, overweight golf balls have been on sale for use as golf teaching aids (see U.S. Pat. No. 4,201,384 to Barber).
Oversized golf balls are also disclosed in New Zealand Patent 192,618 dated Jan. 1, 1980, issued to a predecessor of the present assignee. This patent discloses an oversized golf ball having a diameter between 1.700 and 1.730 inches and an oversized core of resilient material so as to increase the coefficient of restitution. Additionally, the patent discloses that the ball should include a cover having a thickness less than the cover thickness of conventional balls. The patent does not disclose any dimple size or the percentage of surface coverage by the dimples.
Golf balls made by Spalding in 1915 were of a diameter ranging from 1.630 inches to 1.710 inches. While these balls had small shallow dimples, they covered less than 50% of the surface of the ball. Additionally, as the diameter of the ball increased, the weight of the ball also increased.
Golf balls known as the LYNX JUMBO were produced and sold in October of 1979. This ball had a diameter of substantially 1.80 inches. The dimple patterns on the LYNX JUMBO balls had 336 Atti-type dimples with each dimple having a diameter of 0.147 inch and a depth of 0.0148 inch. With this dimple arrangement, 56.02% of the surface area of the ball was covered by the dimples. This ball met with little or no commercial success.
Top-grade golf balls sold in the United States may generally be classified as one of two types; two-piece or three-piece. The two-piece ball, exemplified by the balls sold by Spalding Corporation under the trademark TOP-FLITE, comprises a solid polymeric core and a separately formed cover. The so-called three-piece balls, exemplified by the balls sold under the trademark TITLEIST by the Acushnet Company, comprise a liquid (e.g., TITLEIST TOUR 384) or solid (e.g., TITLEIST DT) center, elastomeric thread windings about the center, and a cover. Although the nature of the cover can, in certain instances, make a significant contribution to the overall coefficient of restitution and initial velocity of a ball (see, for example, U.S. Pat. No. 3,819,768 to Molitor), the initial velocity of two-piece and three-piece balls is determined mainly by the coefficient of restitution of the core. The coefficient of restitution of the core of wound balls can be controlled within limits by regulating the winding tension and the thread and center composition. With respect to two-piece balls, the coefficient of restitution of the core is a function of the properties of the elastomer composition from which it is made. Solid cores today are typically molded using polybutadiene elastomers mixed with acrylate or methacrylate metal salts. High-density fillers such as zinc oxide are included in the core material in order to achieve the maximum U.S.G.A. weight limit.
Improvements in cover and core material formulations and changes in dimple patterns have more or less continually improved golf ball distance for the last 20 years. In co-pending application Ser. No. 08/782,221 filed Jan. 13, 1997 which is owned by the present assignee, now U.S. Pat. No. 6,015,356, there is disclosed a multi-layer golf ball having a diameter of generally 1.68-1.69 inches wherein one or more cover layers contains a heavy weight filler material to enhance the interior perimeter weight of the ball.
Top-grade golf balls, however, must meet several other important design criteria. To successfully compete in today's golf ball market, a golf ball should be resistant to cutting and must be finished well; it should hold a line in putting and should have good click and feel. With a well-designed ball, experienced players can better execute shots involving draw, fade, or abrupt stops, as the situation dictates.